Japanese Laid-open Patent Application Publication No. 2006-226875 discloses a method of detecting a bonding defect of a solder ball by X-ray. In this method, the bonding defect of the solder ball is evaluated by an area, flatness and the like.
In recent years, automatic detection techniques of voids have been developed as a performance evaluation of a BGA (Ball Grid Array). These use statistical procedures as a principle of operation.
For example the number of voids and a ratio of the void area to the solder ball are used as the index indicating the reliability of the solder ball, as detailed in Non-Patent Documents 1 and 2.